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Reverse Evolution in Fish

Reverse evolution in fish, claims an article in EurekAlert, 15 May 2008. Researchers at Fred Hutchinson Cancer Research Centre, Seattle, have studied armour plating in stickleback fish in Lake Washington. Fifty years ago the lake was very murky, due to pollution, but following a massive clean-up the lake is now much clearer. The stickleback fish are more visible to predators in the clear water, so researchers claim the fish have evolved to be more armour plated over the last four decades. In the late 1960s, just after the clean up was complete, only six percent of sticklebacks in Lake Washington had complete covering of armour plating. Today, 49 percent are fully armour plated and 35 percent have a partial covering.

According to EurekAlert, “This rapid, dramatic adaptation is actually an example of evolution in reverse, because the normal evolutionary tendency for freshwater sticklebacks runs toward less armour plating, not more.” The change occurred because “The sticklebacks in Lake Washington contain DNA from both marine (saltwater) fish, which tend to be fully plated, and freshwater sticklebacks, which tend to be low-plated. When environmental pressures called for increased plating, some of the fish had copies of genes that controlled for both low and full plating, and so natural selection favoured the latter.” The amount of plating is under control of a gene called Eda, which comes in two forms: one causes low plating and the other complete plating. Catherine Peichel, who led the study, explained: “Having a lot of genetic variation in the population means that if the environment changes, there may be some gene variant that does better in that new environment than in the previous one, and so nature selects for it. Genetic variation increases the chance of overall survival of the species.”

Editorial Comment: This is another example of the misuse of the word “evolution”. Nothing has evolved here. Before the lake was cleaned up there were both partially and fully armoured fish. All that has happened is that fish with the partial armour gene have been eliminated from the population, leaving those with the full armour gene to breed. As the fish have a lifespan of only about three years, it doesn’t take long for the proportion of fish with the favoured genes to become dominant. This is an example of natural selection, but as we have said many times before, natural selection is not evolution. Selection means to choose from pre-existing options. It does not create the options or change them into other options. (Ref. survival, ichthyology, ecology)